U.S. patent number 10,960,685 [Application Number 16/668,229] was granted by the patent office on 2021-03-30 for image forming apparatus and method for controlling image forming apparatus.
This patent grant is currently assigned to KYOCERA Document Solutions Inc.. The grantee listed for this patent is KYOCERA Document Solutions Inc.. Invention is credited to Toyotsune Inoue, Yasuhiro Michishita, Naoto Miyakoshi, Noriaki Ozawa, Yusuke Takano, Hiroatsu Tamai, Hiroyuki Ueda, Takeshi Watanabe.
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United States Patent |
10,960,685 |
Inoue , et al. |
March 30, 2021 |
Image forming apparatus and method for controlling image forming
apparatus
Abstract
A controller checks ink quantity to be ejected to a specific
area on a first side (specific area ink quantity) and determines an
ink quantity ratio. The specific area is a strip-shaped area
including a side edge on upstream side in a conveying direction of
a paper sheet on the first side. When the ink quantity ratio is
larger than a reference ink quantity ratio, the controller performs
a black conversion process on pixels in a conversion target range.
The conversion target range is a range corresponding to the
specific area in the image data of the first side. The black
conversion process is a process of converting a pixel to which
three color inks, i.e. cyan, magenta, and yellow inks are to be
ejected into a pixel to which only black ink is to be ejected.
Inventors: |
Inoue; Toyotsune (Osaka,
JP), Tamai; Hiroatsu (Osaka, JP), Watanabe;
Takeshi (Osaka, JP), Ueda; Hiroyuki (Osaka,
JP), Michishita; Yasuhiro (Osaka, JP),
Miyakoshi; Naoto (Osaka, JP), Takano; Yusuke
(Osaka, JP), Ozawa; Noriaki (Osaka, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
KYOCERA Document Solutions Inc. |
Osaka |
N/A |
JP |
|
|
Assignee: |
KYOCERA Document Solutions Inc.
(Osaka, JP)
|
Family
ID: |
1000005452610 |
Appl.
No.: |
16/668,229 |
Filed: |
October 30, 2019 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20200139701 A1 |
May 7, 2020 |
|
Foreign Application Priority Data
|
|
|
|
|
Nov 2, 2018 [JP] |
|
|
JP2018-207101 |
Nov 2, 2018 [JP] |
|
|
JP2018-207103 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B41J
2/2103 (20130101); B41J 3/60 (20130101); B41J
2/04586 (20130101) |
Current International
Class: |
B41J
3/60 (20060101); B41J 2/21 (20060101); B41J
2/045 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Seo; Justin
Attorney, Agent or Firm: Stein IP, LLC
Claims
What is claimed is:
1. An image forming apparatus comprising: a line head including a
nozzle for ejecting ink to a conveyed paper sheet, the line head
being fixed; a first conveyor roller pair for conveying the paper
sheet to the line head; a conveyor belt for conveying the paper
sheet in such a manner that the nozzle faces the paper sheet with
an interval therebetween; a switchback roller pair configured to
reverse front and back sides of the paper sheet and to reverse
front and rear edges of the paper sheet for duplex printing; a
second conveyor roller pair for conveying the paper sheet printed
by the line head to the switchback roller pair; a third conveyor
roller pair for conveying the paper sheet switched back by the
switchback roller pair so as to return the paper sheet to the first
conveyor roller pair on upstream side of the line head; and a
controller, wherein a plurality of the line heads are disposed for
individual ink colors, which include cyan, magenta, yellow, and
black at least, and wherein when performing duplex printing, the
controller sets one of front and back sides as a first side and
sets the other side as a second side, starts printing the first
side first and prints the second side after the first side is
printed, checks specific area ink quantity as ink quantity to be
ejected to a specific area on the first side on the basis of image
data of the first side used for printing the first side, determines
an ink quantity ratio by dividing the specific area ink quantity by
a predetermined solid printing ink quantity, and performs a black
conversion process for pixels included in a conversion target range
in the image data of the first side when the determined ink
quantity ratio is larger than a predetermined reference ink
quantity ratio, the specific area is a strip-shaped area including
a side edge on upstream side in the conveying direction of the
paper sheet on the first side, out of side edges facing each other
in a sub-scanning direction, and having a width in the sub-scanning
direction, which is a predetermined distance, the conversion target
range is a range corresponding to the specific area in the image
data of the first side, and the black conversion process is a
process of converting a pixel to which three color inks, i.e. cyan,
magenta, and yellow inks are to be ejected into a pixel to which
only black ink is to be ejected.
2. The image forming apparatus according to claim 1, wherein the
reference ink quantity ratio is an ink quantity ratio when a paper
sheet curl amount becomes the interval, and when the determined ink
quantity ratio is the reference ink quantity ratio or smaller, the
controller does not perform the black conversion process for pixels
included in the conversion target range.
3. The image forming apparatus according to claim 1, wherein the
controller determines front side ink quantity to be ejected to a
front side edge area on the front side, the controller determines
back side ink quantity to be ejected to a back side edge area as a
backside area of the front side edge area on the back side, when
the front side ink quantity is the back side ink quantity or less,
the controller sets the front side as the first side and sets the
back side as the second side, when the front side ink quantity is
more than the back side ink quantity, the controller sets the back
side as the first side and sets the front side as the second side,
and the front side edge area is a strip-shaped area including a
side edge on the upstream side in the sheet conveying direction
when printing the front side, out of side edges facing each other
in a sub-scanning direction, and having a width in the sub-scanning
direction, which is the predetermined distance.
4. The image forming apparatus according to claim 1, wherein a
conveying rotation body is disposed between the line head on the
most upstream side in the sheet conveying direction and the first
conveyor roller pair on the most downstream side in the sheet
conveying direction, and the predetermined distance is a sheet
conveying distance between the conveying rotation body and the line
head on the most upstream side in the sheet conveying
direction.
5. The image forming apparatus according to claim 1, wherein the
controller converts every pixel to which three color inks, i.e.
cyan, magenta, and yellow inks are to be ejected in the conversion
target range into a pixel to which only black ink is to be
ejected.
6. The image forming apparatus according to claim 1, wherein the
controller converts pixels to which three color inks, i.e. cyan,
magenta, and yellow inks are to be ejected in the conversion target
range into pixels to which only black ink is to be ejected, so that
the ink quantity ratio becomes the reference ink quantity ratio or
smaller.
7. The image forming apparatus according to claim 1, wherein the
controller converts a predetermined conversion number of pixels
among pixels to which three color inks, i.e. cyan, magenta, and
yellow inks are to be ejected in the conversion target range, into
pixels to which only black ink is to be ejected.
8. The image forming apparatus according to claim 1, wherein when
the black conversion process is performed, the controller
determines ink quantity after conversion as ink quantity to be
ejected to the specific area, on the basis of the image data of the
first side alter the conversion, the controller divides the
determined ink quantity after conversion by the solid printing ink
quantity so as to determine an ink quantity ratio after conversion,
and when the determined ink quantity ratio after conversion is
larger than the reference ink quantity ratio, the controller allows
the paper sheet after printing one side to wait at the switchback
roller pair for a predetermined wait time.
9. The image forming apparatus according to claim 1, wherein in the
case of printing a plurality of paper sheets successively, when the
controller sets the front side of a first sheet as the first side,
it sets the front side of every page as the first side, and when
the controller sets the back side of the first sheet as the first
side, it sets the back side of every page as the first side.
10. A method for controlling an image forming apparatus, the method
comprising: controlling a fixed line head to eject ink from a
nozzle to a conveyed paper sheet; controlling a first conveyor
roller pair to convey the paper sheet to the line head; controlling
a conveyor belt to convey the paper sheet in such a manner that the
nozzle faces the paper sheet with an interval therebetween;
controls a switchback roller pair to reverse front and back sides
of the paper sheet and to reverse front and rear edges of the paper
sheet for duplex printing; controls to convey the paper sheet
printed by the line head to the switchback roller pair; controls to
convey the paper sheet switched back by the switchback roller pair,
so as to return the paper sheet to the first conveyor roller pair
on upstream side of the line head; disposing a plurality of the
line heads for individual ink colors, including at least cyan,
magenta, yellow, and black; and when performing duplex printing,
setting one of front and back sides as a first side and sets the
other side as a second side, starting printing the first side first
and printing the second side after the first side is printed,
checking specific area ink quantity as ink quantity to be ejected
to a specific area on the first side on the basis of image data of
the first side used for printing the first side, determining an ink
quantity ratio by dividing the specific area ink quantity by a
predetermined solid printing ink quantity, and performing a black
conversion process for pixels included in a conversion target range
in the image data of the first side when the determined ink
quantity ratio is larger than a predetermined reference ink
quantity ratio, wherein the specific area is a strip-shaped area
including a side edge on upstream side in the conveying direction
of the paper sheet on the first side, out of side edges facing each
other in a sub-scanning direction, and having a width in the
sub-scanning direction, which is a predetermined distance, the
conversion target range is a range corresponding to the specific
area in the image data of the first side, and the black conversion
process is a process of converting a pixel to which three color
inks, i.e. cyan, magenta, and yellow inks are to be ejected into a
pixel to which only black ink is to be ejected.
11. An image forming apparatus comprising: a line head including a
nozzle for ejecting ink to a conveyed paper sheet, the line head
being fixed; a first conveyor roller pair for conveying the paper
sheet to the line head; a conveyor belt for conveying the paper
sheet in such a manner that the nozzle faces the paper sheet with
an interval therebetween; a switchback roller pair configured to
reverse front and back sides of the paper sheet and to reverse
front and rear edges of the paper sheet for duplex printing; a
second conveyor roller pair for conveying the paper sheet printed
by the line head to the switchback roller pair; a third conveyor
roller pair for conveying the paper sheet switched back by the
switchback roller pair so as to return the paper sheet to the first
conveyor roller pair on upstream side of the line head; and a
controller, wherein when performing duplex printing, the controller
sets one of front and back sides as a first side and sets the other
side as a second side, starts printing the first side first,
determines first ink quantity as ink quantity to be ejected to a
first area on the first side on the basis of image data of the
first side used for printing the first side, determines second ink
quantity as ink quantity to be ejected to a second area as a
backside area of the first area on the second side, controls to
perform jam prevention printing when the first ink quantity is more
than the second ink quantity, and controls to perform normal duplex
printing when the first ink quantity is the second ink quantity or
less, and when performing the jam prevention printing, the
controller determines an absolute value of a difference between the
first ink quantity and the second ink quantity, controls the line
head to print the first area by the same ink quantity as the
absolute value in printing the first side first time, controls the
switchback roller pair to switchback the paper sheet after printing
the first side so as to return the switched-back paper sheet to the
upstream side of the line head, controls next the line head to
print the entire second side, controls the switchback roller pair
to switchback the paper sheet after printing the second side so as
to return the switched-back paper sheet to upstream side of the
line head, and controls next the line head to print the remaining
area on the first side, and wherein the first area is a
strip-shaped area including a side edge on upstream side in the
conveying direction of the paper sheet when printing the first side
out of side edges facing each other in the sub-scanning direction,
and having a width in the sub-scanning direction, which is a
predetermined distance.
12. The image forming apparatus according to claim 11, wherein when
performing the normal duplex printing, the controller controls to
print the first side first, controls the line head to print the
entire first side in printing the first side, controls the
switchback roller pair to switchback the paper sheet after printing
the first side so as to return the switched-back paper sheet to the
upstream side of the line head, and controls next the line head to
perform printing the entire second side.
13. The image forming apparatus according to claim 11, wherein the
controller divides the determined first ink quantity by a
predetermined solid printing ink quantity so as to determine a
first ink quantity ratio, controls to perform the jam prevention
printing when the first ink quantity is more than the second ink
quantity and when the determined first ink quantity ratio is the
predetermined reference ink quantity ratio or larger, and controls
to perform the normal duplex printing when the determined first ink
quantity ratio is smaller than the reference ink quantity ratio
even when the first ink quantity is more than the second ink
quantity.
14. The image forming apparatus according to claim 13, wherein when
performing the duplex printing, the controller divides ink quantity
ejected to the first area by the solid printing ink quantity so as
to determine an ink quantity ratio of the first area, and when the
determined ink quantity ratio of the first area is the reference
ink quantity ratio or larger, the controller allows the paper
sheet, which has been printed on the first side first time and is
on the way returning to the upstream side of the line head, to wait
at the switchback roller pair for a predetermined wait time.
15. The image forming apparatus according to claim 11, wherein a
conveying rotation body is disposed between the line head on the
most upstream side in the sheet conveying direction and the first
conveyor roller pair on the most downstream side in the sheet
conveying direction, and the predetermined distance is a sheet
conveying distance between the conveying rotation body and the line
head on the most upstream side in the sheet conveying
direction.
16. The image forming apparatus according to claim 11, wherein in
the case of printing a plurality of paper sheets successively, when
the controller sets the front side of a first sheet as the first
side, it sets the front side of every page as the first side, and
when the controller sets the back side of the first sheet as the
first side, it sets the back side of every page as the first side.
Description
INCORPORATION BY REFERENCE
This application is based upon and claims the benefit of priority
from the corresponding Japanese Patent Application Nos. 2018-207101
and 2018-207103 filed Nov. 2, 2018, the entire contents of which
are hereby incorporated by reference.
BACKGROUND
The present disclosure relates to an image forming apparatus that
includes a line head and performs image formation (printing or
drawing) using ink.
There is an image forming apparatus that performs printing using
ink. The image forming apparatus using ink may cause bleed through
of ink that is ejected to a paper sheet and soaks into the paper
sheet. In addition, a part of the paper sheet at which ink is
adhered is bulged. The bulging may cause curl or ripple (cockling).
An example of an inkjet recording apparatus as described below is
known, in which bleed through, curl, and ripple are taken into
consideration.
An inkjet recording apparatus capable of performing duplex printing
is described, in which the number of print passes in simplex
printing is different from that in duplex printing with respect to
the same area, i.e. the latter is larger than the former. This
technique focuses attention on the fact that as the number of print
passes is larger, bleed through becomes less, curl amount becomes
less, and cockling amount also becomes less. The number of print
passes is changed between simplex printing and for duplex printing,
so that the optimal number of print passes is set for each of
them.
A paper sheet absorbs ejected ink. The part absorbing ink is
bulged. As a result, an edge portion of a paper sheet in a
sub-scanning direction (sheet conveying direction) may be largely
curled (furled). The curl occurs in the direction opposite to the
bulged surface (the surface to which the ink is ejected). For
instance, when the ink is ejected to the upper surface of the paper
sheet, an edge portion of the paper sheet is curled downward. In
general, as more ink is ejected to the edge portion of the paper
sheet, the curl amount becomes more.
When performing duplex printing, the head first ejects ink to one
side of the paper sheet. After printing one side, front and back
sides of the paper sheet are reversed. The paper sheet after
reversing front and back sides is sent back to upstream of the
head. Then, the paper sheet after printing one side is conveyed to
the head. The head ejects ink to the other side of the paper sheet.
Thus, both sides of the paper sheet are printed.
As distance between a nozzle (head) and a paper sheet is larger, a
deviation of landing position of ink becomes larger. Therefore,
distance between the nozzle and the paper sheet (paper sheet
conveying path) is set small. For instance, the distance is set a
few millimeters or smaller. As the distance is small, there is a
problem that a paper sheet may be jammed in the gap between the
head and the conveying path in duplex printing, when the curl
amount of the edge portion of the paper sheet after printing one
side is large. When the paper sheet is jammed, it is necessary to
remove the jammed paper sheet. Then, productivity of the image
forming apparatus is lowered. In addition, the jammed paper sheet
may damage the head.
In order to reduce bleed through or curl, the inkjet recording
apparatus described above increases the number of print passes. For
instance, it increases the number of print passes by four to eight
times per side. This increases the number of print passes for
printing one sheet in duplex printing. This may cause substantial
reduction in productivity (printing speed). A problem of
productivity remains.
SUMMARY
An image forming apparatus according to a first aspect of the
present disclosure includes a line head, a first conveyor roller
pair, a conveyor belt, a switchback roller pair, a second conveyor
roller pair, a third conveyor roller pair, and a controller. The
line head includes a nozzle for ejecting ink to a conveyed paper
sheet and is fixed. The first conveyor roller pair conveys the
paper sheet to the line head. The conveyor belt conveys the paper
sheet in such a manner that the nozzle faces the paper sheet with
an interval therebetween. The switchback roller pair reverses front
and back sides of the paper sheet and reverses the front and rear
edges of the paper sheet for duplex printing. The second conveyor
roller pair conveys the paper sheet printed by the line head to the
switchback roller pair. The third conveyor roller pair conveys the
paper sheet switched back by the switchback roller pair so as to
return the paper sheet to the first conveyor roller pair on the
upstream side of the line head. A plurality of the line heads are
disposed for individual ink colors. The ink colors include cyan,
magenta, yellow, and black at least. In duplex printing, the
controller sets one of front and back sides as a first side and
sets the other side as a second side. The controller starts
printing the first side first and prints the second side after the
first side is printed. On the basis of image data of the first side
used for printing the first side, the controller checks specific
area ink quantity as ink quantity to be ejected to a specific area
on the first side. The controller determines an ink quantity ratio
by dividing the specific area ink quantity by a predetermined solid
printing ink quantity. When the determined ink quantity ratio is
larger than a predetermined reference ink quantity ratio, the
controller performs a black conversion process for pixels included
in a conversion target range in the image data of the first side.
The specific area is a strip-shaped area including a side edge on
upstream side in the conveying direction of the paper sheet on the
first side, out of side edges facing each other in a sub-scanning
direction, and having a width in the sub-scanning direction, which
is a predetermined distance. The conversion target range is a range
corresponding to the specific area in the image data of the first
side. The black conversion process is a process of converting a
pixel to which three color inks, i.e. cyan, magenta, and yellow
inks are to be ejected into a pixel to which only black ink is to
be ejected.
In addition, an image forming apparatus according to a second
aspect of the present disclosure includes a line head, a first
conveyor roller pair 51, a conveyor belt, a switchback roller pair,
a second conveyor roller pair, a third conveyor roller pair 90, and
a controller. The line head includes a nozzle for ejecting ink to a
conveyed paper sheet and is fixed. The first conveyor roller pair
51 conveys the paper sheet to the line head. The conveyor belt
conveys the paper sheet in such a manner that the nozzle faces the
paper sheet with an interval therebetween. The switchback roller
pair reverses front and back sides of the paper sheet and reverses
front and rear edges of the paper sheet for duplex printing. The
second conveyor roller pair conveys the paper sheet printed by the
line head to the switchback roller pair. The third conveyor roller
pair 90 conveys the paper sheet switched back by the switchback
roller pair so that the paper sheet is returned to the first
conveyor roller pair 51 on the upstream side of the line head. In
duplex printing, the controller sets one of front and back sides as
a first side and sets the other side as a second side. The
controller starts printing the first side. On the basis of image
data of the first side used for printing the first side, the
controller determines first ink quantity as ink quantity to be
ejected to a first area on the first side. The controller
determines second ink quantity as ink quantity to be ejected to a
second area as a backside area of the first area on the second
side. When the first ink quantity is more than the second ink
quantity, the controller controls to perform jam prevention
printing. When the first ink quantity is the second ink quantity or
less, the controller controls to perform normal duplex printing.
When performing the jam prevention printing, the controller
determines an absolute value of a difference between the first ink
quantity and the second ink quantity. In printing the first side
first time, the controller controls the line head to print the
first area by the same ink quantity as the absolute value. The
controller controls the switchback roller pair to switchback the
paper sheet after printing the first side. The controller controls
to return the switched-back paper sheet to upstream side of the
line head. Next, the controller controls the line head to print the
entire second side. The controller controls the switchback roller
pair to switchback the paper sheet after printing the second side.
The controller controls to return the switched-back paper sheet to
upstream side of the line head. Next, the controller controls the
line head to print the remaining area on the first side. The first
area is a strip-shaped area including a side edge on upstream side
in the conveying direction of the paper sheet when printing the
first side out of side edges facing each other in the sub-scanning
direction, and having a width in the sub-scanning direction, which
is a predetermined distance.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing an example of a printer according to an
embodiment.
FIG. 2 is a diagram showing an example of the printer according to
the embodiment.
FIG. 3 is a diagram showing an example of a process flow in simplex
printing by the printer according to the embodiment.
FIG. 4 is a diagram showing an example of a setting flow for first
and second sides in duplex printing by the printer according to the
embodiment.
FIG. 5 is a diagram showing an example of a front side edge area
and a back side edge area according to the embodiment.
FIG. 6 is a diagram showing an example of a process flow in duplex
printing by the printer according to the embodiment.
FIG. 7 is a diagram showing an example of a process flow in duplex
printing by the printer according to the embodiment.
FIG. 8 is a diagram showing an example of paper sheet curl.
FIG. 9 is a diagram showing an example of curl amount with respect
to an ink quantity ratio.
FIG. 10 is a diagram showing an example of curl amount variation
with respect to time from ink ejection.
FIG. 11 is a diagram showing an example of type determination of
duplex printing performed by the printer according to a variation
example of the present disclosure.
FIG. 12 is a diagram showing an example of first and second areas
according to the variation example.
FIG. 13 is a diagram showing an example of paper sheet curl.
FIG. 14 is a diagram showing an example of a process of normal
duplex printing by the printer according to the variation
example.
FIG. 15 is a diagram showing the example of the process of normal
duplex printing by the printer according to the variation
example.
FIG. 16 is a diagram showing an example of a process of jam
prevention printing by the printer according to the variation
example.
FIG. 17 is a diagram showing the example of the process of jam
prevention printing by the printer according to the variation
example.
DETAILED DESCRIPTION
The present disclosure describes prevention of paper sheet jamming
at a head due to curl in duplex printing, while maintaining
productivity. With reference to FIGS. 1 to 10, one example of an
image forming apparatus according to an embodiment of the present
disclosure is described below. In addition, with reference to FIGS.
11 to 17, one example of an image forming apparatus according to a
variation of the present disclosure is described. A printer 100 is
exemplified as the image forming apparatus for description. The
printer 100 is an inkjet type. Note that the printer 100 may be a
multifunction peripheral including a scanner, for example.
(Outline of Printer 100)
First, with reference to FIGS. 1 and 2, outline of the printer 100
according to the embodiment and the variation is described. The
printer 100 includes a controller 1, a storage medium 2, an
operation panel 3, a printer unit 4, and a communication circuit
10. The controller 1 controls individual portions of the printer
100. The controller 1 includes a control circuit 11 and an image
processing circuit 12. The control circuit 11 is a CPU, for
example. The control circuit 11 performs calculation and processing
on the basis of a control program and control data stored in the
storage medium 2. The storage medium 2 includes a nonvolatile
storage device such as a ROM or a storage (such as an HDD or a
flash ROM), and a volatile storage device such as a RAM.
The operation panel 3 includes a display panel 31 and a touch panel
32. The display panel 31 displays setting screens and information.
The controller 1 controls the display panel 31 to display images
for operation such as keys, buttons, and tabs. The touch panel 32
detects a touch operation to the display panel 31. On the basis of
an output from the touch panel 32, the controller 1 recognizes an
image for operation that is operated. The controller 1 recognizes a
setting operation performed by a user.
The printer 100 includes the printer unit 4. The controller 1
controls operation of the printer unit 4. The printer unit 4
includes a sheet feeder 4a, a first conveyor 5, an image former 6,
a second conveyor 7, a switchback unit 8, and a third conveyor 9,
The sheet feeder 4a stores a stack of paper sheets. The sheet
feeder 4a includes a sheet feed roller 41. The sheet feed roller 41
contacts the uppermost paper sheet of the stack of paper sheets
stored in the sheet feeder 4a. A sheet feed motor (not shown) is
provided for driving the sheet feed roller 41 to rotate. In a print
job, the controller 1 controls the sheet feed motor to rotate so as
to drive the sheet feed roller 41 to rotate. In this way, the sheet
feeder 4a feeds a paper sheet to the first conveyor 5.
The first conveyor 5 conveys the paper sheet. The controller 1
controls the first conveyor 5 to convey the paper sheet fed from
the sheet feeder 4a to the image former 6. In FIG. 2, paper sheet
conveying paths are shown by thick lines. Along the conveying
paths, a conveying rotation body 50 and a plurality of first
conveyor roller pairs 51 are disposed. The conveying rotation body
50 is a roller. A first conveying motor (not shown) is disposed for
driving these rotating bodies to rotate. In the print job, the
controller 1 controls the first conveying motor to rotate so as to
drive the conveying rotation body 50 and the first conveyor roller
pairs 51 to rotate.
The first conveyor 5 includes a conveyor unit 53. The conveyor unit
53 includes a driving roller 54, a plurality of driven rollers 55,
and a conveyor belt 56. The conveyor belt 56 is stretched around
the driving roller 54 and the driven rollers 55. In the print job,
the controller 1 controls a belt motor to rotate. The belt motor
drives the driving roller 54 to rotate. As a result, the paper
sheet fed from the sheet feeder 4a is conveyed on the conveyor belt
56. Note that the conveyor unit 53 includes a suction unit. The
suction unit sucks the paper sheet on the conveyor belt 56 by
sucking air or using electrostatic force. The suction unit fixes
position of the paper sheet and distance between each nozzle and
the paper sheet. When performing printing, the controller 1
controls the suction unit to work.
The image former 6 ejects ink to the conveyed paper sheet so as to
record an image. The image former 6 includes a plurality of line
heads 60. Specifically, the printer 100 includes four line heads 60
(6Bk, 6C, 6M, and 6Y). The line head 6Bk ejects black ink. The line
head 6C ejects cyan ink. The line head 6M ejects magenta ink. The
line head 6Y ejects yellow ink.
The line heads 60 are disposed above the conveyor belt 56. Position
of each line head 60 is fixed. Each line head 60 includes a
plurality of nozzles. The nozzles are arranged in a main scanning
direction (a direction perpendicular to the conveying direction).
Each nozzle ejects ink to the conveyed paper sheet. An opening of
each nozzle faces the conveyor belt 56. When performing printing,
the first conveyor 5 conveys the paper sheet to the line heads 60
and conveys the paper sheet in such a manner facing the nozzle.
An interval W (gap) is formed between each line head 60 and the
conveyor belt 56 (see FIG. 2). The paper sheet enters into this
interval W. The interval W has a predetermined value. The interval
W is approximately 1 to a few millimeters, for example. The ink
ejected from the nozzle lands on the conveyed paper sheet. In this
way, an image is recorded (formed). Note that an ink tank for
supplying ink is disposed for each line head 60.
The controller 1 controls the second conveyor 7 to convey the paper
sheet after passing the line heads 60. The second conveyor 7
conveys the paper sheet to the discharge tray 73 or to the
switchback unit 8. The second conveyor 7 includes a plurality of
second conveyor roller pairs 70, a first switching guide 71, and a
second switching guide 72. A second conveying motor (not shown) is
disposed to drive the second conveyor roller pairs 70 to rotate.
The first switching guide 71 and the second switching guide 72 are
guide plates for switching the paper sheet conveying path. The
first switching guide 71 guides the paper sheet to the discharge
tray 73 or to the switchback unit 8. A first switching motor (not
shown) is disposed to drive the first switching guide 71 to swing.
The second switching guide 72 guides the paper sheet to the
switchback unit 8 or to the first conveyor 5 (upstream of the image
former 6). A second switching motor (not shown) is disposed to
drive the second switching guide 72 to swing.
The switchback unit 8 includes a switchback roller pair 80. For
duplex printing, the controller 1 controls the switchback unit 8 to
reverse front and back sides of the paper sheet and to reverse
front and rear edges of the paper sheet.
The third conveyor 9 conveys the paper sheet switched back by the
switchback unit 8. The third conveyor 9 includes the third conveyor
roller pair 90. A third conveying motor (not shown) is disposed to
drive the third conveyor roller pair 90 to rotate. The controller 1
controls the third conveyor 9 to convey the switched-back paper
sheet. The third conveyor 9 returns the switched-back paper sheet
to upstream side of the line head 60. The third conveyor 9 allows
the switched-back paper sheet to join the first conveyor 5.
The controller 1 is connected to the communication circuit 10. The
communication circuit 10 includes communication hardware (a
connector, a communication control circuit, and a communication
memory). The communication memory stores communication software.
The communication circuit 10 communicates with a computer 200. The
computer 200 is a PC or a server, for example. The controller 1
receives print data from the computer 200. The print data includes
print setting information and data described in page description
language, for example. The print setting information is information
for setting a print job. The print setting performed by a user with
the computer 200 is included in the print setting information. For
instance, when setting is performed with the computer 200 to
perform duplex printing, the print data includes the print setting
information indicating to perform duplex printing.
The controller 1 (the image processing circuit 12) analyzes data
described in page description language included in the print data.
On the basis of the data described in page description language,
the controller 1 generates print image data (raster data), The
controller 1 performs image processing on the basis of the print
image data. Finally, the controller 1 performs image processing
such as halftone processing and generates image data for ink
ejection. The image data for ink ejection is data indicating nozzle
positions to eject ink and ejection timings. On the basis of the
image data for ink ejection, the controller 1 controls the line
head 60 to eject ink for each line.
(Process of Simplex Printing)
Next, with reference to FIG. 3, one example of a process flow of
simplex printing by the printer 100 according to the embodiment and
the variation is described. Note that when printing successively on
a plurality of paper sheets, the controller 1 may perform the
process of FIG. 3 in parallel.
First, on the basis of the received print data, the controller 1
generates the image data for ink ejection for a page to be printed
(Step #11). Next, the controller 1 controls the sheet feeder 4a to
feed the paper sheet (Step #12). In this way, the paper sheet is
fed from the sheet feeder 4a. Next, the controller 1 controls the
first conveyor 5 to convey the paper sheet to the image former 6
(Step #13). When the paper sheet reaches the image former 6, the
controller 1 controls each line head 60 to eject ink on the basis
of the generated image data for ink ejection (Step #14). By ink
ejection from each line head 60, printing (drawing) on one side of
the paper sheet is completed.
Then, the controller 1 controls the second conveyor 7 to convey the
paper sheet to the discharge tray 73 (Step #15). At this time, the
controller 1 controls the plurality of second conveyor roller pairs
70 to rotate. In addition, the controller 1 controls the first
switching guide 71 to swing so that the paper sheet is discharged
onto the discharge tray 73. In other words, the controller 1
controls the first switching guide 71 to close the passage to the
switchback unit 8. Finally, the second conveyor 7 discharges the
printed paper sheet onto the discharge tray 73 (Step #16, discharge
in direction A in FIG. 2). In this way, simplex printing of one
page paper sheet is completed (END).
(Setting of First and Second Sides)
Next, one example of a setting flow for first and second sides in
duplex printing by the printer 100 according to the embodiment is
described with reference to FIGS. 4 and 5. The flow of FIG. 4
starts when duplex printing is started on the basis of the received
print data. In this case, the print data includes print setting
information defining that duplex printing is to be performed. The
controller 1 analyzes the print setting information and recognizes
that duplex printing is to be performed.
First, the controller 1 generates image data for ink ejection of
each page of front and back sides on the basis of the received
print data (Step #21). In duplex printing, the print data includes
front side page data described in page description language and
back side page data described in page description language. The
controller 1 (the image processing circuit 12) generates print
image data (raster data) for each of front side and back side
pages. Further, the controller 1 generates image data for ink
ejection for each of front side and back side pages. In color
printing, the controller 1 generates image data for ink ejection of
C, M, Y, and Bk colors for the front side. In addition, the
controller 1 generates image data for ink ejection of C, M, Y, and
Bk colors for the back side, too.
Next, on the basis of the image data for ink ejection of the first
page front side, the controller 1 determines front side ink
quantity (Step #22). On the basis of the image data for ink
ejection of the first page back side, the controller 1 determines
back side ink quantity (Step #23). The front side ink quantity is
quantity of ink to be ejected to a front side edge area F1 on the
front side. In addition, the back side ink quantity is quantity of
ink to be ejected to a back side edge area F2 on the back side.
As shown in FIG. 5, the front side edge area F1 includes a side
edge on upstream side in the sheet conveying direction (rear edge
side) out of side edges facing each other in the sub-scanning
direction. The upstream side in the sheet conveying direction (rear
edge side) is upstream side when printing the front side. When
printing the back side by switchback, the front side edge area F1
becomes the downstream side in the sheet conveying direction (front
edge side). The front side edge area F1 has a width in the
sub-scanning direction, which is a predetermined distance L1. The
front side edge area F1 is a strip-shaped area. As shown in FIG. 5,
the back side edge area F2 is a backside area of the front side
edge area F1. The front side edge area F1 and the back side edge
area F2 have the same area size.
Further, the predetermined distance L1 may be the same as a sheet
conveying distance between the roller closest to the line head 60
on the most upstream side in the sheet conveying direction (the
conveying rotation body 50) and the line head 60 on the most
upstream side in the sheet conveying direction. In other words, the
predetermined distance L1 may be a sheet conveying distance between
the conveying rotation body 50 and the line head 60 on the most
upstream side. In FIG. 2, the sheet conveyor roller closest to the
line head 60 is denoted by 50. In FIG. 2, the predetermined
distance L1 is a distance between the conveying rotation body 50
and a side surface of the line head 60 on the most upstream side in
the sheet conveying direction, the side surface being parallel to
the main scanning direction. In this way, the predetermined
distance L1 may be a distance from the nip between the conveying
rotation body 50 and the conveyor belt 56 to a start point of the
interval W between the conveyor belt 56 and the line head 6Y in the
sheet conveying direction.
Calculation of the front side ink quantity and the back side ink
quantity is described. First, quantity of ink to be ejected to one
pixel is determined in advance for each color. Further, in the
printer 100 of this embodiment, the quantity of ink to be ejected
to one pixel is the same (or may be different) among colors. For
instance, the quantity of ink to be ejected to one pixel is
approximately 5 to 7.5 picolitters for each color.
The controller 1 counts the number of pixels to eject ink for each
color in the area corresponding to the front side edge area F1 in
the image data for ink ejection of the front side. The controller 1
determines the number of pixels to eject ink for each of cyan,
yellow, magenta, and black inks. The controller 1 determines the
sum of the numbers of pixels of individual colors. The controller 1
multiplies quantity of ink to be ejected to one pixel of one color
and the determined sum, so as to calculate the front side ink
quantity (Step #22).
In addition, the controller 1 counts the number of pixels to eject
ink for each color in the area corresponding to the back side edge
area F2 in the image data for ink ejection of the back side. The
controller 1 determines the number of pixels to eject ink for each
of cyan, yellow, magenta, and black inks. The controller 1
determines the sum of the numbers of pixels of individual colors.
The controller 1 multiplies quantity of ink to be ejected to one
pixel of one color and the determined sum, so as to calculate the
back side ink quantity (Step #23).
Next, the controller 1 checks whether or not the front side ink
quantity is the back side ink quantity or less (Step #24). In other
words, the controller 1 checks which one of the front side edge
area F1 and the back side edge area F2 has more ink ejection
quantity.
When the front side ink quantity is the back side ink quantity or
less (Yes in Step #24), the controller 1 sets the front side as a
first side and sets the back side as a second side (Step #25). On
the contrary, when the front side ink quantity is more than the
back side ink quantity (No in Step #24), the controller 1 sets the
back side as the first side and sets the front side as the second
side (Step #26), When Step #25 or Step #26 is performed, this flow
is finished (END). The controller 1 sets one of the front and back
sides as the first side and sets the other side as the second side.
After that, the controller 1 starts printing the first side of each
paper sheet, and prints the second side after the first side is
printed. In this way, the controller 1 determines which one of the
front and back sides should be printed first.
Note that in a print job of performing duplex printing a plurality
of paper sheets successively, when the front side of the first
sheet is set as the first side, the controller 1 sets the front
side of every page as the first side. When the back side of the
first sheet is set as the first side, the controller 1 sets the
back side of every page as the first side. In this way, the
discharged paper sheets have sorted front and back sides in all
pages.
(Flow of Duplex Printing)
Next, with reference to FIGS. 6 to 10, one example of flow of
duplex printing by the printer 100 according to the embodiment is
described. After setting the first and second sides, the controller
1 checks specific area ink quantity as ink quantity for a specific
area (Step #31). Here, the specific area includes a side edge on
upstream side in the sheet conveying direction (rear edge side) of
the paper sheet out of side edges facing each other in the
sub-scanning direction. The upstream side in the sheet conveying
direction (rear edge side) means upstream side when printing the
first side. The specific area has a width in the sub-scanning
direction, which is the predetermined distance L1. The specific
area is a strip-shaped area.
When the front side is the first side, the front side edge area F1
corresponds to the specific area. When the back side is the first
side, the specific area includes a side edge on upstream side in
the sheet conveying direction (rear edge side) when printing the
back side, out of side edges facing each other in the sub-scanning
direction. When the back side is the first side, the upstream side
in the sheet conveying direction (rear edge side) is the upstream
side when printing the back side.
When the front side is the first side, the controller 1 sets the
front side ink quantity as the specific area ink quantity. When the
back side is the first side, the controller 1 counts the number of
pixels to eject ink for each color in the area corresponding to the
specific area in the image data for ink ejection of the back side.
The controller 1 determines the number of pixels to eject ink for
each of cyan, yellow, magenta, and black inks. The controller 1
determines the sum of the numbers of pixels of individual colors.
The controller 1 multiplies the quantity of ink to be ejected to
one pixel of one color and the determined sum, so as to calculate
the specific area ink quantity (Step #31).
Further, the controller 1 calculates an ink quantity ratio (Step
#32). The controller 1 calculates the ink quantity ratio by
dividing the specific area ink quantity by solid printing ink
quantity 21. The solid printing ink quantity 21 is determined in
advance. The storage medium 2 stores the solid printing ink
quantity 21 in a nonvolatile manner (see FIG. 1). The controller 1
performs the calculation using the solid printing ink quantity 21
stored in the storage medium 2.
The solid printing ink quantity 21 is ink quantity when ejecting
ink to all pixels of all colors in the specific area. In other
words, the solid printing ink quantity 21 is ink consumption
quantity when ejecting C, M, Y, and Bk inks to all pixels in the
specific area. The number of all pixels in the specific area, the
ink ejection quantity to one pixel of one color, and 4 (4 colors)
are multiplied, and thus the solid printing ink quantity 21 can be
calculated (ink quantity 400%). The ink quantity ratio indicates a
ratio of ink quantity in the specific area to ink quantity when
performing 4-color solid printing.
Further, the controller 1 checks whether or not the determined ink
quantity ratio is more than a reference ink quantity ratio 22 (Step
#33). The reference ink quantity ratio 22 is an ink quantity ratio
when the paper sheet curl amount becomes the same as the interval W
between the line head 60 (nozzle) and the conveyor belt 56 (paper
sheet). The reference ink quantity ratio 22 is determined in
advance. The storage medium 2 stores the reference ink quantity
ratio 22 in a nonvolatile manner. The controller 1 refers to the
reference ink quantity ratio 22 stored in the storage medium 2.
First, with reference to FIG. 8, paper sheet curl is described. The
ink is ejected to the paper sheet. The paper sheet absorbs the
ejected ink. A part that absorbed ink is bulged. When expansion
rate is different between one side and the other side of the paper
sheet, the paper sheet is curled. FIG. 8 shows an example in which
the ink is ejected to the upper surface. For instance, when the ink
is ejected to the upper surface on the upstream side in the sheet
conveying direction, the upstream side edge of the paper sheet is
curled (curved) downward.
The curl amount is a sag amount of a paper sheet edge. The curl
amount is a lift amount (height) of the paper sheet edge in a state
where the curled part is curled upward. It can also be said that
the curl amount is a distance between the paper sheet edge and the
horizontal surface in the vertical direction when the paper sheet
is placed on the horizontal surface. Further, as shown in FIG. 9,
as more ink is ejected to the specific area, the curl amount
becomes more. It is because more liquid is absorbed by the paper
sheet so that an expansion degree is increased.
Here, one example of the reference ink quantity ratio 22 is shown
by broken lines in FIG. 9. By repeating experiment, it is possible
to check the ink quantity ratio at which the curl amount becomes
equal to the interval W between the line head 60 (nozzle) and the
conveyor belt 56 (paper sheet). When duplex printing is performed
when the ink quantity ratio is equal to the reference ink quantity
ratio 22, probability of occurrence of jamming of the paper sheet
at the line head 60 is increased. The reference ink quantity ratio
22 becomes a reference for determining whether or not the paper
sheet is jammed at the line head 60.
When the determined ink quantity ratio is larger than the reference
ink quantity ratio 22 (Yes in Step #33), the controller 1 performs
a black conversion process for pixels included in a conversion
target range in the image data of the first side (image data for
ink ejection of the first side) (Step #34). The conversion target
range is the range corresponding to the specific area in the image
data for ink ejection of the first side.
On the contrary, when the determined ink quantity ratio is the
reference ink quantity ratio 22 or smaller (No in Step #33), the
controller 1 skips Step #34 and Step #35. In other words, the
controller 1 does not perform the black conversion process for
pixels in the conversion target range.
The black conversion process is a process of converting a pixel to
which three color inks, i.e. cyan, magenta, and yellow inks are to
be ejected into a pixel to which only black ink is to be ejected.
When reproducing black color, cyan, magenta, and yellow inks may be
superimposed at one pixel. The pixel at which cyan, magenta, and
yellow inks are to be superimposed is converted into a pixel to
which only black ink is to be ejected. Specifically, the controller
1 converts a pixel at which three color inks, i.e. cyan, magenta,
and yellow inks are superimposed in the image data for cyan,
magenta, and yellow ink ejection into a non-ejection pixel (white).
In addition, the controller 1 converts a pixel in the image data
for black ink ejection, at the same position as the pixel converted
into the non-ejection pixel, into an ejection pixel (black). In
this way, ink quantity to be used for this pixel is reduced to 1/3.
By performing the black conversion process, curl amount in the
specific area can be reduced.
Here, the controller 1 (image processing circuit 12) may convert
every pixel in the conversion target range, to which three color
inks, i.e. cyan, magenta, and yellow inks are ejected into a pixel
to which only black ink is to be ejected (first method). In this
case, the controller 1 reduces ink quantity to be ejected to the
specific area as much as possible.
In addition, the controller 1 (image processing circuit 12) may
convert pixels to which three color inks, i.e. cyan, magenta, and
yellow inks are to be ejected in the conversion target range into
pixels to which only black ink is to be ejected, so that the ink
quantity ratio becomes the reference ink quantity ratio 22 or
smaller (second method). In the second black conversion method, a
target ink quantity ratio is determined in advance. The target ink
quantity ratio may be a reference ink quantity ratio 22.
Alternatively, the target ink quantity ratio may be smaller than
the reference ink quantity ratio 22.
For instance, the controller 1 calculates an absolute value of a
difference between the determined ink quantity ratio and the target
ink quantity ratio. The controller 1 multiplies the absolute value
and the solid printing ink quantity 21 so as to calculate a
reduction target value. The reduction target value indicates ink
quantity to be reduced so that the ink quantity ratio becomes the
target ink quantity ratio. Dividing the reduction target value by
decreased amount of ink used for one pixel after the black
conversion process, the controller 1 can determine the number of
pixels for which the black conversion process should be performed.
The controller 1 performs the black conversion process for the
determined number of pixels for which the black conversion process
should be performed. Note that, when the number of pixels for which
the black conversion process can be performed is smaller than the
number of pixels for which the black conversion process should be
performed, the controller 1 performs the black conversion process
for all pixels for which the black conversion process can be
performed.
Alternatively, the controller 1 (image processing circuit 12) may
convert pixels of a predetermined conversion number (upper limit
number) out of pixels to which three color inks, i.e. cyan,
magenta, and yellow inks are to be ejected in the conversion target
range, into pixels to which only black ink is to be ejected (third
method). The black conversion process may change tint or color
shade of the image. By setting the upper limit conversion number,
change in tint or color shade of the image can be reduced.
The operation panel 3 may accept selection of the black conversion
process to be used from the first to third methods. In this case,
the controller 1 (image processing circuit 12) performs the
selected black conversion process.
When the black conversion process is performed, the controller 1
determines ink quantity ratio after conversion on the basis of the
image data of the first side (image data for ink ejection of the
first side) after the conversion (Step #35). Specifically, the
controller 1 determines ink quantity after conversion as ink
quantity to be ejected to the specific area. The controller 1
counts the number of pixels to eject ink for each color in the area
corresponding to the specific area in the image data for ink
ejection of the first side after the conversion. The controller 1
determines the number of pixels to eject ink for each of cyan,
yellow, magenta, and black inks. The controller 1 determines the
sum of the numbers of pixels of individual colors. The controller 1
multiplies the quantity of ink to be ejected to one pixel of one
color and the determined sum, so as to calculate the ink quantity
after conversion. Further, the controller 1 divides the determined
ink quantity after conversion by the solid printing ink quantity
21, so as to calculate the ink quantity ratio after conversion.
Next, the controller 1 controls the sheet feeder 4a to feed the
paper sheet (Step #36). In this way, the paper sheet is fed from
the sheet feeder 4a. Next, the controller 1 controls the first
conveyor 5 to convey the paper sheet to the image former 6 (Step
#37). When the paper sheet reaches the image former 6, the
controller 1 controls each head 60 to perform ink ejection on the
basis of the image data for ink ejection of the first side (Step
#38). After each line head 60 performs ink ejection, printing
(drawing) on one side of the paper sheet is completed.
Further, the controller 1 controls the second conveyor 7 to convey
the paper sheet to the switchback unit 8 (Step #39). The controller
1 allows the paper sheet to enter the switchback unit 8. The
controller 1 controls the plurality of second conveyor roller pairs
70 to rotate. In addition, the controller 1 controls the first
switching guide 71 to swing to the position for sending the paper
sheet to the switchback unit 8. In other words, the controller 1
controls the first switching guide 71 to open the passage to the
switchback unit 8. In addition, the controller 1 controls the
second switching guide 72 to swing so that the paper sheet can
enter the switchback unit 8. As a result, the paper sheet is
conveyed in direction B in FIG. 2.
Further, the controller 1 controls the switchback unit 8 to perform
the switchback operation (Step #310). First, the controller 1
controls the switchback roller pair 80 to rotate so that the paper
sheet enters to the back of the switchback unit 8. Further, the
controller 1 stops the switchback roller pair 80 before the paper
sheet pass a nip between the switchback roller pair 80. When the
rear edge of the paper sheet passes a branch point of the second
conveyor 7, the switchback unit 8, and the third conveyor 9, the
controller 1 stops the switchback roller pair 80. In this way, in
the following conveyance, an edge in the specific area of the paper
sheet becomes the downstream side in the sheet conveying direction
(front edge side). The edge in the specific area first enters the
line head 60 (the interval W).
Further, the controller 1 checks whether or not the black
conversion process has been performed (Step #311). When the black
conversion process has been performed (Yes in Step #311), the
controller 1 checks whether or not the ink quantity ratio after
conversion is larger than the reference ink quantity ratio 22 (Step
#312). When the ink quantity ratio after conversion is larger than
the reference ink quantity ratio 22 (Yes in Step #312), the
controller 1 allows the paper sheet after printing one side to wait
at the switchback unit 8 for a predetermined wait time 23 (Step
#313).
As shown in FIG. 10, there is a tendency that as elapsed time from
ink ejection becomes longer, the curl amount of the paper sheet
edge becomes smaller. It may be possible to avoid paper sheet
jamming at the line head 60 by delaying entrance of the
switched-back paper sheet to the line head 60 after ink ejection to
the first side. The storage medium 2 stores the wait time 23 in a
nonvolatile manner. The controller 1 refers to the wait time 23
stored in the storage medium 2. The wait time 23 can be determined
appropriately. It may be possible to determine a plurality of sets
of the wait time 23. For instance, as the ink quantity ratio after
conversion is larger, the wait time 23 may be defined longer. In
addition, when the ink is ejected to the specific area by the solid
printing ink quantity 21, the time required for the curl amount in
the specific area to become the interval W between the nozzle and
the conveyor belt 56 or less may be defined as the wait time
23.
After waiting of the paper sheet after printing one side (Step
#313), the controller 1 returns the paper sheet (after printing one
side) to the upstream side of the line head 60 (Step #314). In
addition, when the black conversion process is not performed (No in
Step #311), or when the ink quantity ratio after conversion is not
larger than the reference ink quantity ratio 22 (No in Step #312),
the controller 1 returns the paper sheet (after printing one side)
to the upstream side of the line head 60 without waiting (without
setting the wait time 23) (Step #314).
The controller 1 controls the second switching guide 72 to swing to
angle for guiding the paper sheet to the first conveyor 5 (to the
upstream of the image former 6). In addition, the controller 1
controls the switchback roller pair 80 to rotate in the direction
for discharging the paper sheet from the switchback unit 8. In
addition, the controller 1 controls the third conveyor roller pair
90 (third conveying motor) to rotate so that the paper sheet can
join the conveying path of the first conveyor 5.
In order to start printing the second side, the controller 1
controls the first conveyor 5 to convey the paper sheet to the
image former 6 (Step #315). The paper sheet, whose front and rear
edges are reversed and front and back sides are reversed from those
when printing the first side, is conveyed. When the switched-back
paper sheet reaches the image former 6, the controller 1 controls
each head 60 to perform ink ejection on the basis of image data for
ink ejection of the second side (Step #316). After each line head
60 performs ink ejection, printing (drawing) on the second side of
the paper sheet is completed.
Further, the controller 1 controls the second conveyor 7 to convey
the paper sheet to the discharge tray 73 (Step #317). In a short
time, the paper sheet after duplex printing is discharged onto the
discharge tray 73. Next, the controller 1 checks whether or not the
print job is completed (Step #318). In other words, the controller
1 checks whether or not the duplex printing to be performed
according to the print job has been finished. When the print job is
completed (Yes in Step #318), this flow is finished (END). When the
print job is not completed (No in Step #318), the flow returns to
Step #31.
In this way, the image forming apparatus (printer 100) according to
the embodiment includes the line head 60, the first conveyor 5
(first conveyor roller pairs 51), the switchback unit 8 (switchback
roller pair 80), the second conveyor 7 (second conveyor roller pair
70), the third conveyor 9 (third conveyor roller pair 90), and the
controller 1. The line head 60 includes the nozzle for ejecting ink
to the conveyed paper sheet. The line head 60 is fixed. The first
conveyor 5 includes the first conveyor roller pairs 51. The first
conveyor 5 conveys the paper sheet to the line head 60. The first
conveyor 5 conveys the paper sheet in such a manner that the nozzle
faces the paper sheet with the interval W therebetween. The
switchback unit 8 includes the switchback roller pair 80. The
switchback unit 8 reverses front and back sides of the paper sheet
and reverses front and rear edges of the paper sheet for duplex
printing. The second conveyor 7 conveys the paper sheet printed by
the line head 60 to the switchback unit 8. The third conveyor 9
conveys the paper sheet switched back by the switchback unit 8. The
third conveyor 9 returns the paper sheet to the first conveyor 5 on
the upstream side of the line head 60. A plurality of the line
heads 60 are disposed for individual ink colors. The ink colors
include, at least, cyan, magenta, yellow, and black. In duplex
printing, the controller 1 sets one of the front and back sides as
the first side and sets the other side as the second side. The
controller 1 starts printing the first side first and prints the
second side after the first side is printed. On the basis of the
image data of the first side used for printing the first side, the
controller 1 checks specific area ink quantity as ink quantity to
be ejected to the specific area on the first side. The controller 1
divides the specific area ink quantity by the predetermined solid
printing ink quantity 21 so as to determine the ink quantity ratio.
When the determined ink quantity ratio is larger than the
predetermined reference ink quantity ratio 22, the controller 1
performs the black conversion process for pixels included in the
conversion target range in the image data of the first side. The
specific area is a strip-shaped area including a side edge on the
upstream side in the conveying direction of the paper sheet on the
first side out of the side edges facing each other in the
sub-scanning direction, and having a width in the sub-scanning
direction, which is a predetermined distance L1. The conversion
target range is a range corresponding to the specific area in the
image data of the first side. The black conversion process is a
process of converting a pixel to which three color inks, i.e. cyan,
magenta, and yellow inks are to be ejected into a pixel to which
only black ink is to be ejected.
On the basis of the ink quantity ejected to the specific area, the
ink quantity ratio can be determined. The specific area is an area
on the upstream side in the sheet conveying direction (rear edge
side in the sub-scanning direction) when printing the first side.
When the paper sheet is switched back for duplex printing (when
printing the second side), the specific area becomes the downstream
side in the sheet conveying direction (front edge side in the
sub-scanning direction). In other words, the specific area is a
part that reaches first the line head 60 when printing the second
side. Further, by comparison between the determined ink quantity
ratio and the reference ink quantity ratio 22, it can be determined
whether or not curl in the specific area is large when printing the
second side. In other words, in a second pass (when the paper sheet
passes below the line head 60), it can be determined whether or not
curl is large at the front edge of the paper sheet to be printed on
the second side (downstream side in the conveying direction).
When printing the second side, when it is predicted that curl in
the specific area is large, the black conversion process can be
performed. The black conversion process can reduce curl amount in
the specific area when printing the second side (in the second
pass). As the curl amount can be reduced, paper sheet jamming at
the line head 60 can be prevented. In addition, it is not required
to increase the number of print passes for reducing the curl. In
duplex printing, paper sheet jamming at the head can be prevented
while maintaining productivity.
The reference ink quantity ratio 22 is an ink quantity ratio when
the paper sheet curl amount becomes the interval W between the line
head 60 and the conveyor belt 56. When the determined ink quantity
ratio is the reference ink quantity ratio 22 or less, the
controller 1 does not perform the black conversion process for
pixels included in the conversion target range. When the curl
amount is such a degree that paper sheet jamming does not occur at
the line head 60, it is possible to avoid performing the black
conversion process. The black conversion process can be performed
only in cases where curl occurs in such a degree that paper sheet
jamming occurs when printing the second side for duplex printing
(in the second pass).
The controller 1 determines the front side ink quantity to be
ejected to the front side edge area F1 on the front side. The
controller 1 determines the back side ink quantity to be ejected to
the back side edge area F2 on the back side as a backside area of
the front side edge area F1. When the front side ink quantity is
the back side ink quantity or less, the controller 1 sets the front
side as the first side and sets the back side as the second side.
When the front side ink quantity is more than the back side ink
quantity, the controller 1 sets the back side as the first side and
sets the front side as the second side. The front side edge area F1
is a strip-shaped area including a side edge on the upstream side
in the sheet conveying direction when printing the front side out
of side edges facing each other in the sub-scanning direction, and
having a width in the sub-scanning direction, which is a
predetermined distance L1. One of the front and back sides, which
requires less ink used for the area corresponding to the specific
area, can be set as the first side. When printing the second side
for duplex printing (in the second pass), it is possible to start
printing first the side having less curl at the edge on the
downstream side in the sheet conveying direction (front edge side
in the sub-scanning direction).
The conveying rotation body 50 is disposed between the line head 60
on the most upstream side in the sheet conveying direction and the
first conveyor roller pair 51 on the most downstream side in the
sheet conveying direction. The predetermined distance L1 is a sheet
conveying distance between the conveying rotation body 50 and the
line head 60 on the most upstream side in the sheet conveying
direction. The conveying rotation body 50 contacts the paper sheet.
After the paper sheet passes the conveying rotation body 50, there
is no member that presses the paper sheet. As a result, after the
paper sheet passes the nip of the conveying rotation body 50, curl
at the edge of the paper sheet becomes obvious (appears again). On
the basis of the part curling after passing the conveying rotation
body 50 closest to the line head 60 until reaching the line head
60, it is possible to determine the widths of the specific area,
the front side edge area F1, and the back side edge area F2 in the
sub-scanning direction.
The controller 1 may convert every pixel in the conversion target
range, to which three color inks, i.e. cyan, magenta, and yellow
inks are to be ejected, into a pixel to which only black ink is to
be ejected. It is possible to reduce quantity of ink to be ejected
to the specific area on the first side to the least. It is possible
to reduce curl in the specific area as much as possible.
The controller 1 may convert pixels in the conversion target range,
to which three color inks, i.e. cyan, magenta, and yellow inks are
to be ejected, into pixels to which only black ink is to be
ejected, so that the ink quantity ratio becomes the reference ink
quantity ratio 22 or smaller. When printing the second side for
duplex printing (in the second pass), curl at the edge on the
downstream side in the sheet conveying direction (front edge side
in the sub-scanning direction) can be reduced to an extent that
paper sheet jamming does not occur. In addition, the number of
pixels for which the black conversion process is performed can be
reduced as much as possible.
The controller 1 may convert a predetermined conversion number of
pixels in the conversion target range, to which three color inks,
i.e. cyan, magenta, and yellow inks are to be ejected, into pixels
to which only black ink is to be ejected. When printing the second
side for duplex printing (in the second pass), curl can be reduced
to an extent that paper sheet jamming does not occur at the line
head 60. It is possible to perform the black conversion process for
a certain number of pixels.
When the black conversion process is performed, the controller 1
determines the ink quantity after conversion as ink quantity to be
ejected to the specific area, on the basis of the image data of the
first side after the conversion. The controller 1 divides the
determined ink quantity after conversion by the solid printing ink
quantity 21 so as to calculate the ink quantity ratio after
conversion. When the determined ink quantity ratio after conversion
is larger than the reference ink quantity ratio 22, the controller
1 allows the paper sheet after printing one side to wait at the
switchback unit 8 (switchback roller pair 80) for predetermined
wait time 23. As elapsed time from ink ejection becomes longer, the
curl amount becomes smaller in general. After the black conversion
process is performed, it may still occur that ink is ejected to the
specific area on the first side to an extent that paper sheet
jamming occurs at the line head 60. In this case, the paper sheet
can wait at the switchback unit 8. When printing the second side
for duplex printing (in the second pass), it is possible to allow
the paper sheet to enter below the line head 60 after reducing curl
amount at the edge on the downstream side in the sheet conveying
direction (front edge side in the sub-scanning direction).
In the case of printing a plurality of paper sheets successively,
when the front side of the first sheet is set as the first side,
the controller 1 sets the front side of every page as the first
side. When the back side of the first sheet is set as the first
side, the controller 1 sets the back side of every page as the
first side. A relationship between front and back sides of the
printed paper sheet can be unified for all pages.
(Variations)
Next, with reference to FIGS. 11 to 17, one example of an image
forming apparatus according to a variation is described. Also in
this variation, the printer 100 is exemplified as the image forming
apparatus and is described. The image forming apparatus according
to the variation has a similar structure to the image forming
apparatus according to the embodiment. In other words, the same
hardware can be used. The same name and the same numeral of each
member as those in the embodiment are used in the following
description.
(Setting of First and Second Sides in Duplex Printing)
First, setting of the first and second sides in the variation is
described. In duplex printing, odd pages in the print data are
printed on the front sides. In addition, even pages (odd pages on
the front sides plus one page) in the print data are printed on the
back sides. In duplex printing, the controller 1 sets one of the
front and back sides of pages to be printed as the first side. The
controller 1 sets the other side as the second side. In other
words, the controller 1 sets one of the odd page and the even page
next to the odd page as the first side and sets the other page as
the second side.
In duplex printing, the controller 1 starts printing the first side
first. Here, in a job of performing duplex printing a plurality of
paper sheets successively, when the paper sheets of the printed
matter discharged onto the discharge tray 73 have sorted front and
back sides and are stacked in order from the first page, it is not
required to sort the paper sheets of the printed matter.
On the other hand, in printing, the controller 1 allows the paper
sheets to pass below the line head 60. Further, the printer 100 of
the variation has two types of duplex printing. One type is jam
prevention printing (details thereof are described later). The
other type is normal duplex printing (details thereof are described
later).
The jam prevention printing according to the variation is a print
process for eliminating paper sheet jamming at the line head 60
similarly to the embodiment. In the jam prevention printing
according to the variation, printing of a side to be printed first
(the first side) is divided into two times of printing. This point
is different from the embodiment. In the jam prevention printing,
the switchback is performed two times. In addition, the paper sheet
passes the line head 60 three times. In contrast, in the normal
duplex printing, the number of passes is at least two. In the
normal duplex printing, the number of switchbacks is at least one
time.
In order to avoid necessity of sorting the printed matter after
duplex printing, it is preferred that the first page is discharged
first onto the discharge tray 73. In addition, it is preferred that
the paper sheets are discharged with odd pages facing down on the
discharge tray 73.
Therefore, in the duplex printing according to the variation, the
controller 1 controls to print the first paper sheet (page) first.
For instance, the controller 1 controls to print odd pages on one
sides of the paper sheets and to print next pages to the odd pages
(even pages) on the other sides. For instance, the first and second
pages are printed on the first paper sheet. The third and fourth
pages are printed on the next paper sheet.
The printer 100 of the variation may sometimes perform the jam
prevention printing. At this time, the printer 100 can set the
front side (odd page) as the first side. When the front side is set
as the first side, after the two times of switchback in the jam
prevention printing, the paper sheet with the front side facing up
passes the line head 60 in the third pass. The second conveyor 7
discharges the paper sheet onto the discharge tray 73 with the
front and back sides reversed from those when passing the line head
60. Therefore, the paper sheet is discharged with the front side
facing down onto the discharge tray 73 (face down). In this way, in
duplex printing, the controller 1 may start printing the front side
(odd page) first.
However, when the front side is set as the first side, in the
normal duplex printing, when the paper sheet is discharged onto the
discharge tray 73 just after the duplex printing is completed
(after the second side has been printed entirely), the paper sheet
is discharged with the back side facing down (with the front side
facing up). Therefore, when the front side is set as the first
side, in the normal duplex printing, after the second side has been
printed, the controller 1 controls the switchback unit 8 to perform
switchback of the paper sheet. Further, the controller 1 controls
the third conveyor 9 and the first conveyor 5 to allow the paper
sheet to pass the line head 60 again. After that, the controller 1
controls the second conveyor 7 to discharge the paper sheet onto
the discharge tray 73. In this way, the order of pages and the
front and back sides of the paper sheets discharged onto the
discharge tray 73 are sorted.
Note that in the normal duplex printing, the back side may be set
as the first side. When the back side is set as the first side,
after the switchback one time in the normal duplex printing, the
paper sheet passes the line head 60 with the front side facing up
in the second pass. The second conveyor 7 discharges the paper
sheet onto the discharge tray 73 with reversing the front and back
sides of the paper sheet, and hence the paper sheet can be
discharged onto the discharge tray 73 with the front side facing
down.
It is possible to perform the jam prevention printing with setting
the back side as the first side. In this case, when the paper sheet
is discharged onto the discharge tray 73 just after the duplex
printing is completed (after the first side has been printed
entirely), the paper sheet is discharged with the back side facing
down (with the front side facing up). Therefore, in the jam
prevention printing with setting the back side as the first side,
the controller 1 controls the switchback unit 8 to perform
switchback of the paper sheet after the first side has been printed
entirely. Further, the controller 1 controls the third conveyor 9
and the first conveyor 5 to allow the paper sheet to pass the line
head 60 again. After that, the controller 1 controls the second
conveyor 7 to discharge the paper sheet onto the discharge tray 73.
The number of passes in the jam prevention printing becomes four.
Thus, the front and back sides and the order of pages of the paper
sheets discharged onto the discharge tray 73 are sorted.
In this way, in duplex printing, the controller 1 may start
printing with setting the back side (even page) as the first side.
In the following description, in consideration of the jam
prevention printing, an example in which the front side (a side on
which an odd page is printed) is set as the first side is
described.
(Determination of Duplex Printing to be Performed)
Next, with reference to FIGS. 11 to 13, one example of a flow of
determining a type of duplex printing to be performed by the
printer 100 according to the variation is described. In this
variation, the controller 1 determines one of the jam prevention
printing and the normal duplex printing as the duplex printing to
be performed on the paper sheet. In the variation, the controller 1
performs this determination for each of the paper sheets. When
performing duplex printing a plurality of paper sheets
successively, the controller 1 determines which one of duplex
printing should be performed for each (one page) of the paper
sheets.
The controller 1 generates image data for ink ejection of the first
and second sides on the basis of the received print data (Step
#41). The duplex printing uses data of the front page (odd page)
described in page description language for the next duplex printing
and data of the back page (front odd page plus one page) described
in page description language in the print data. The controller 1
(the image processing circuit 12) generates front and back print
image data (raster data). On the basis of the print image data, the
controller 1 generates front and back image data for ink ejection.
In case of color printing, the controller 1 generates C, M, Y, and
Bk image data for ink ejection of the front side. In addition, the
controller 1 generates C, M, Y, and Bk image data for ink ejection
of the back side, too.
The controller 1 determines first ink quantity (Step #42). The
controller 1 determines the first ink quantity on the basis of
image data to be used for printing the first side (image data for
ink ejection of the first side). The first ink quantity is ink
quantity to be ejected to a first area G1 on the first side.
As shown in FIG. 5, the first area G1 includes the side edge on the
upstream side in the sheet conveying direction (rear edge side) out
of the side edges facing each other in the sub-scanning direction.
The upstream side in the sheet conveying direction (rear edge side)
is the upstream side when printing the first side. The first area
G1 has a width in the sub-scanning direction, which is the
predetermined distance L1. The first area G1 is a strip-shaped
area.
The predetermined distance L1 is the same as that in the
embodiment. The predetermined distance L1 may be the sheet
conveying distance between the conveying rotation body 50 and the
line head 60 on the most upstream side.
Next, the controller 1 determines second ink quantity (Step #43).
The controller 1 determines the second ink quantity on the basis of
image data to be used for printing the second side (image data for
ink ejection of the second side). The second ink quantity is ink
quantity to be ejected to a second area G2 on the second side. As
shown in FIG. 12, the second area G2 is a backside area of the
first area G1. The first area G1 and the second area G2 have the
same area size.
Calculation of the first ink quantity and the second ink quantity
is described. First, also in the printer 100 according to the
variation, quantity of ink to be ejected to one pixel is determined
for each color. In addition, in the printer 100, the quantity of
ink to be ejected to one pixel is the same (or may be different)
among colors. For instance, the quantity of ink to be ejected to
one pixel is approximately 5 to 7.5 picolitters for each color.
The controller 1 counts the number of pixels to eject ink for each
color in the area corresponding to the first area G1 in the image
data for ink ejection of the first side. The controller 1
determines the number of pixels to eject ink for each of cyan,
yellow, magenta, and black inks. The controller 1 determines the
sum of the numbers of pixels of individual colors. The controller 1
multiplies the quantity of ink to be ejected to one pixel of one
color and the determined sum so as to calculate the first ink
quantity (Step #42)
In addition, the controller 1 counts the number of pixels to eject
ink for each color in the area corresponding to the second area G2
in the image data for ink ejection of the back side. The controller
1 determines the number of pixels to eject ink for each of cyan,
yellow, magenta, and black inks. The controller 1 determines the
sum of the numbers of pixels of individual colors. The controller 1
multiplies the quantity of ink to be ejected to one pixel of one
color and the determined sum so as to calculate the second ink
quantity (Step #43).
The controller 1 checks whether or not the first ink quantity is
the second ink quantity or less (Step #44). When the first ink
quantity is the second ink quantity or less (Yes in Step #44), the
controller 1 determines to perform the normal duplex printing (Step
#45). After Step #45, setting of type of the duplex printing on the
paper sheet is completed (END).
On the contrary, when the first ink quantity is more than the
second ink quantity (No in Step #44), the controller 1 determines a
first ink quantity ratio (Step #46). The controller 1 divides the
determined first ink quantity by the solid printing ink quantity 21
determined in advance so as to calculate the first ink quantity
ratio. The storage medium 2 stores the solid printing ink quantity
21 in a nonvolatile manner (see FIG. 1). The controller 1 performs
the calculation using the solid printing ink quantity 21 stored in
the storage medium 2.
The solid printing ink quantity 21 in the variation is ink quantity
when ejecting all color inks to all pixels in the first area G1 or
the second area G2. In other words, the solid printing ink quantity
21 is ink consumption quantity when ejecting C, M, Y, and Bk inks
to all pixels in the first area G1 or the second area G2. The
number of all pixels in the first area G1 or the second area G2,
ink ejection quantity for one color and one pixel, and 4 (4 colors)
are multiplied, and thus the solid printing ink quantity 21 can be
calculated (ink quantity 400%). Each ink quantity ratio indicates a
ratio of ink quantity in the first area G1 or the second area G2 to
ink quantity when performing 4-color solid printing.
Further, the controller 1 checks whether or not the first ink
quantity ratio is the reference ink quantity ratio 22 or larger
(Step #47). The reference ink quantity ratio 22 is an ink quantity
ratio when the paper sheet curl amount becomes the same as the
interval W between the line head 60 and the conveyor belt 56. The
reference ink quantity ratio 22 is determined in advance. This
point is the same as the embodiment. The controller 1 refers to the
reference ink quantity ratio 22 stored in the storage medium 2 in a
nonvolatile manner.
When the first ink quantity is more than the second ink quantity
and when the determined first ink quantity ratio is the reference
ink quantity ratio 22 or larger (Yes in Step #47), the controller 1
determines to perform the jam prevention printing (Step #48). After
Step #48, setting of type of the duplex printing on the paper sheet
is completed (END). Even when the first ink quantity is more than
the second ink quantity, when the determined first ink quantity
ratio is the reference ink quantity ratio 22 or smaller (No in Step
#47), the controller 1 determines to perform the normal duplex
printing (Step #45).
Here, with reference to FIG. 13, paper sheet curl in the printer
100 of the variation is described. In the paper sheet, a part that
absorbed ink is bulged. When expansion rate of paper fiber is
different between one side and the other side of the paper sheet,
the paper sheet is curled. FIG. 13 shows an example in which ink is
ejected to the first area G1 on the upper surface. For instance,
when ink is ejected to the upper surface on the upstream side in
the sheet conveying direction, the upstream side edge (first area
G1) of the paper sheet is curled (curved) downward.
As shown in FIG. 13, the curl amount is a lift amount (height) of
the paper sheet edge. It can also be said that the curl amount is a
distance between the paper sheet edge and the horizontal surface in
the vertical direction when the paper sheet is placed on the
horizontal surface with the first area G1 facing back (in the same
manner as described above with reference to FIG. 8). Note that the
reference ink quantity ratio 22 according to the variation is the
same as the reference ink quantity ratio 22 according to the
embodiment. The above description with reference to FIG. 9 can be
incorporated. Here, the description is omitted.
When the first ink quantity ratio is smaller than the reference ink
quantity ratio 22, even when the entire first area G1 on the first
side is printed in the first pass, the paper sheet is not jammed at
the line head 60. It is not required to divide ink ejection to the
first side into a plurality of times of ejection. Therefore, when
the first ink quantity ratio is smaller than the reference ink
quantity ratio 22, the controller 1 determines to perform the
normal duplex printing.
Note that it may be possible not to perform Step #46 and Step #47.
In this case, when the first ink quantity is the second ink
quantity or less (Yes in Step #44), the controller 1 determines to
perform the normal duplex printing. When the first ink quantity is
more than the second ink quantity (No in Step #44), the controller
1 determines to always perform the jam prevention printing.
In addition, it may be also possible that the controller does not
check whether or not the first ink quantity is the second ink
quantity or less (does not perform Step #44). It may be also
possible that when the first ink quantity ratio is larger than the
reference ink quantity ratio 22, the controller 1 determines to
perform the jam prevention printing. In addition, it may be also
possible that when the first ink quantity ratio is the reference
ink quantity ratio 22 or smaller, the controller 1 determines to
perform the normal duplex printing.
(Normal Duplex Printing)
Next, with reference to FIGS. 14 and 15, one example of the normal
duplex printing process by the printer 100 according to the
variation is described. After setting the first and second sides,
the controller 1 controls the sheet feeder 4a to feed one paper
sheet (Step #51). In this way, the paper sheet is fed from the
sheet feeder 4a. Until the print job of the duplex printing is
completed, the paper sheets are fed repeatedly.
Next, the controller 1 controls the first conveyor 5 to convey the
paper sheet to the image former 6 (Step #52). When the paper sheet
reaches the image former 6, the controller 1 controls each head 60
to perform ink ejection on the basis of image data for ink ejection
of the first side (Step #53). When performing the normal duplex
printing, the controller 1 controls the line head 60 to perform
printing the entire first side. The controller 1 controls to eject
the first ink quantity of ink to the first area G1 Printing
(drawing) on one side (first side) of the paper sheet is
completed.
Further, the controller 1 controls the second conveyor 7 to convey
the paper sheet to the switchback unit 8 (Step #54). The controller
1 performs the same process as Step #39. As a result, the paper
sheet is conveyed in the direction B in FIG. 2.
The controller 1 controls the switchback unit 8 to perform the
switchback operation (Step #55). The controller 1 controls the
switchback unit 8 to perform the same operation as Step #310 in
FIG. 6. In this way, in the following conveyance, an edge portion
having the first area G1 and the second area G2 of the paper sheet
becomes the downstream side in the sheet conveying direction (front
edge side). When the paper sheet is sent back to the image former
6, the edge portion having the first area G1 and the second area G2
enters first to the line head 60 (the interval W between the nozzle
and the conveyor belt 56).
Further, the controller 1 determines ink quantity ratio of the
first area G1 (Step #56). The ink quantity to be ejected to the
first area G1 (first ink quantity) is divided by the solid printing
ink quantity 21, and thus the ink quantity ratio of the first area
G1 is calculated. In normal duplex printing, the ink quantity to be
ejected to the first area G1 may become large. For instance, even
when the first ink quantity is the second ink quantity or less,
when both the first ink quantity and the second ink quantity are
relatively large, the ink quantity to be ejected to the first area
G1 may become large.
The controller 1 checks whether or not the ink quantity ratio of
the first area G1 is the reference ink quantity ratio 22 or larger
(Step #57). When the ink quantity ratio of the first area G1 is the
reference ink quantity ratio 22 or larger (Yes in Step #57), the
controller 1 allows the paper sheet after printing one side (paper
sheet after passing the line head 60 one time) to wait at the
switchback unit 8 for a predetermined wait time 23 (Step #58).
There is a tendency that as elapsed time from ink ejection becomes
longer, the curl amount at the paper sheet edge becomes smaller
(see FIG. 10). By temporarily stopping conveyance after ink
ejection to the first side (first area G1), paper sheet jamming at
the line head 60 may be prevented. The wait time 23 in the
variation may be the same as the wait time 23 in the embodiment
described above.
After waiting the wait time 23 (Step #58), the controller 1 returns
the switched-back paper sheet (after printing one side) to the
upstream side of the line head 60 (Step #59). On the contrary, when
the ink quantity ratio of the first area G1 is smaller than the
reference ink quantity ratio 22 (No in Step #57), after the
switchback is completed, the controller 1 soon returns the
switched-back paper sheet (after printing one side) to the upstream
side of the line head 60 (Step #59). The controller 1 controls the
second switching guide 72 to swing so as to guide the paper sheet
to the first conveyor 5 (upstream of the image former 6). In
addition, the controller 1 controls the switchback roller pair 80
to rotate in the direction discharging the paper sheet from the
switchback unit 8 (reverse rotation). In addition, the controller 1
controls the third conveyor roller pair 90 (third conveying motor)
to rotate so that the paper sheet can join the conveying path of
the first conveyor 5.
In order to start printing the second side, the controller 1
controls the first conveyor 5 to convey the paper sheet to the
image former 6 (Step #510). The front and rear edges are reversed
from those in printing the first side. The front and back sides are
reversed from those in printing the first side. When the
switched-back paper sheet reaches the image former 6, the
controller 1 controls each head 60 to perform ink ejection on the
basis of the image data for ink ejection of the second side (Step
#511). After each line head 60 performs ink ejection, printing
(drawing) on the second side of the paper sheet is completed.
When the paper sheet is discharged in this state, it is discharged
with the front side (odd page) facing up. Therefore, the controller
1 controls the second conveyor 7 to convey the paper sheet to the
switchback unit 8 (Step #512). The controller 1 performs the same
process as Step #39 or Step #54. As a result, the paper sheet is
conveyed in the direction B in FIG. 2.
The controller 1 controls the switchback unit 8 to perform the
switchback operation (Step #513). The controller 1 controls the
switchback unit 8 to perform the same operation as Step #310 in
FIG. 6 or Step #55.
The controller 1 returns the switched-back paper sheet (the paper
sheet after printing one side) to the upstream side of the line
head 60 (Step #514). The controller 1 controls the second switching
guide 72 to swing so as to guide the paper sheet to the first
conveyor 5 (upstream of the image former 6). In addition, the
controller 1 controls the switchback roller pair 80 to rotate in
the direction discharging the paper sheet to from the switchback
unit 8 (reverse rotation). In addition, the controller 1 controls
the third conveyor roller pair 90 (third conveying motor) to
rotate, so that the paper sheet can join the conveying path of the
first conveyor 5. Next, the controller 1 controls the first
conveyor 5 to convey the paper sheet (Step #515). The controller 1
allows the paper sheet to pass the image former 6. As printing is
completed, the controller 1 does not allow the line heads 60 to
eject ink.
Further, the controller 1 controls the second conveyor 7 to convey
again the switched-back paper sheet to the discharge tray 73 (Step
#516). In a short time, the paper sheet after duplex printing is
discharged onto the discharge tray 73. The paper sheet is
discharged with the front side facing down. Next, the controller 1
checks whether or not the print job is completed (Step #517). In
other words, the controller 1 checks whether or not the duplex
printing to be performed according to the print job has been
finished. When the print job is completed (Yes in Step #517), this
flow is finished (END). When the print job is not completed (No in
Step #517), the flow returns to Step #51.
(Jam Prevention Printing)
Next, with reference to FIGS. 16 and 17, one example of the jam
prevention printing process by the printer 100 according to the
variation is described. When starting the jam prevention printing
after setting the first and second sides, the controller 1
determines the absolute value of a difference between the first ink
quantity and the second ink quantity for the paper sheet to be
duplex printed (Step #61). For instance, when the first ink
quantity is 100 and the second ink quantity is 70, the determined
absolute value is 30.
The controller 1 controls the sheet feeder 4a to feed one paper
sheet (Step #62). The paper sheet is fed from the sheet feeder 4a,
Until the print job of the duplex printing is completed, the paper
sheets are fed repeatedly. Next, the controller 1 controls the
first conveyor 5 to convey the fed paper sheet to the image former
6 (Step #63).
When the paper sheet reaches the image former 6, the controller 1
controls the line head 60 to perform printing the first side first
time on the basis of the image data for ink ejection of the first
side (Step #64). At this time, the controller 1 controls the line
head 60 to perform printing by the same ink quantity as the
determined absolute value for the first area G1 on the first
side.
In Step #64, the controller 1 may control the line head 60 to print
the entire area other than the first area G1 on the first side. In
addition, the controller 1 may control to print only the first area
G1 in printing the first side first time. In this case, in printing
the first side second time performed later, other area than the
first area G1 on the first side is printed.
Further, the controller 1 controls the second conveyor 7 to convey
the paper sheet to the switchback unit 8 (Step #65). The controller
1 performs the same process as Step #39, Step #54, or Step #512. As
a result, the paper sheet is conveyed in the direction B in FIG.
2.
Further, the controller 1 controls the switchback unit 8 to perform
the switchback operation (Step #66). The controller 1 controls
switchback unit 8 to perform the same operation as Step #310 in
FIG. 6, Step #55, or Step #513. In this way, in the following
conveyance, the edge portion having the first area G1 and the
second area G2 of the paper sheet becomes the downstream side in
the sheet conveying direction (front edge side). When the paper
sheet is sent back to the image former 6, the edge portion having
the first area G1 and the second area G2 first enters the line head
60 (the interval W between the nozzle and the conveyor belt
56).
Further, the controller 1 determines the ink quantity ratio of the
first area G1 (Step #67). The controller 1 divides the ink quantity
ejected actually to the first area G1 (absolute value) by the solid
printing ink quantity 21, so as to calculate the ink quantity ratio
of the first area G1 when printing the first side first time. Also
in the jam prevention printing, the ink quantity to be ejected to
the first area G1 may be large. For instance, when the first ink
quantity is the second ink quantity or less, and when the
difference between the first ink quantity and the second ink
quantity is relatively large, the ink quantity to be ejected to the
first area G1 when printing the first side first time may be
large.
The controller 1 checks whether or not the ink quantity ratio of
the first area G1 is the reference ink quantity ratio 22 or larger
(Step #68). When the ink quantity ratio of the first area G1 is the
reference ink quantity ratio 22 or larger (Yes in Step #68), the
controller 1 allows the paper sheet after printing one side (the
paper sheet after passing the line head 60 one time) to wait at the
switchback unit 8 for the predetermined wait time 23 (Step
#69).
After waiting the wait time 23 (Step #69), the controller 1 returns
the switched-back paper sheet (after printing one side) to the
upstream side of the line head 60 (Step #610). Alternatively, when
the ink quantity ratio of the first area G1 is smaller than the
reference ink quantity ratio 22 (No in Step #68), the controller 1
returns the switched-back paper sheet (after printing one side) to
the upstream side of the line head 60 soon after the switchback is
completed (Step #610). The controller 1 controls the second
switching guide 72 to swing so as to guide the paper sheet to the
first conveyor 5 (upstream of the image former 6). In addition, the
controller 1 controls the switchback roller pair 80 to rotate in
the direction discharging the paper sheet from the switchback unit
8 (reverse rotation). In addition, the controller 1 controls the
third conveyor roller pair 90 (third conveying motor) to rotate, so
that the paper sheet can join the conveying path of the first
conveyor 5.
In order to start printing the second side, the controller 1
controls the first conveyor 5 to convey the paper sheet to the
image former 6 (Step #611). The paper sheet, whose front and rear
edges are reversed and front and back sides are reversed from those
in printing the first side, is conveyed. When the switched-back
paper sheet reaches the image former 6, the controller 1 controls
each head 60 to perform printing (ink ejection) on the second side
on the basis of the image data for ink ejection of the second side
(Step #612). The controller 1 controls the line head 60 to perform
printing the entire second side.
After each line head 60 performs ink ejection, printing (drawing)
on the second side of the paper sheet is completed. By printing the
second side, the second area G2 is printed. As ink is ejected to
the second area G2 too, the second area G2 is also expanded. The
expansion rate of the first area G1 becomes close to that of the
second area G2. The curl amount does not become large.
Here, the first side still has a remaining part to be printed.
Therefore, the controller 1 controls the second conveyor 7 to
convey the paper sheet to the switchback unit 8 (Step #613). The
controller 1 allows the paper sheet to enter the switchback unit 8.
The controller 1 performs the same process as Step #39, Step #54,
Step #512, or Step #65. As a result, the paper sheet is conveyed m
the direction B in FIG. 2.
Further, the controller 1 controls the switchback unit 8 to perform
the switchback operation (Step #614). The controller 1 performs the
same process as Step #39, Step #54, Step #512, or Step #66.
The controller 1 returns the switched-back paper sheet (after
printing one side) to the upstream side of the line head 60 (Step
#615). The controller 1 controls the second switching guide 72 to
swing so as to guide the paper sheet to the first conveyor 5
(upstream of the image former 6). The controller 1 controls the
switchback roller pair 80 to rotate in the direction discharging
the paper sheet from the switchback unit 8 (reverse rotation). The
controller 1 controls the third conveyor roller pair 90 (third
conveying motor) to rotate, so that the paper sheet can join the
conveying path of the first conveyor 5.
Next, the controller 1 controls the first conveyor 5 to convey the
paper sheet (Step #616). When the paper sheet reaches the image
former 6, the controller 1 controls the line head 60 to perform
printing the first side second time on the basis of the image data
for ink ejection of the first side (Step #617). The controller 1
controls the line head 60 to perform printing the remaining part on
the first side (printing of an unprinted part).
The controller 1 controls the line head 60 to print the unprinted
part in the first area G1 on the first side. The controller 1
controls the line head 60 to perform ink ejection of ink quantity
obtained by subtracting the absolute value from the first ink
quantity. For other areas than the first area G1, the controller 1
controls the line head 60 to print the unprinted part.
Further, the controller 1 controls the second conveyor 7 to convey
the switched-back paper sheet to the discharge tray 73 (Step #618).
The duplex printed paper sheet is discharged onto the discharge
tray 73 in a short time. The first side is the front side, and the
switchback has been performed two times. Therefore, the paper sheet
is discharged with the front side facing down. Next, the controller
1 checks whether or not the print job is completed (Step #619). In
other words, the controller 1 checks whether or not the duplex
printing to be performed according to the print job has been
finished. When the print job is completed (Yes in Step #619), this
flow is finished (END). When the print job is not completed (No in
Step #619), the flow returns to Step #61.
In this way, the image forming apparatus (printer 100) according to
the variation includes the line head 60, the first conveyor 5
(first conveyor roller pairs 51), the switchback unit 8 (switchback
roller pair 80), the second conveyor 7 (second conveyor roller pair
70), the third conveyor 9 (third conveyor roller pair 90), and the
controller 1. The line head 60 includes the nozzle for ejecting ink
to the conveyed paper sheet. The line head 60 is fixed. The first
conveyor 5 includes the first conveyor roller pairs 51. The first
conveyor 5 conveys the paper sheet to the line head 60. The first
conveyor 5 conveys the paper sheet in such a manner that the nozzle
faces the paper sheet. The switchback unit 8 includes the
switchback roller pair 80. The switchback unit 8 reverses front and
back sides of the paper sheet and reverses front and rear edges of
the paper sheet for duplex printing. The second conveyor 7 conveys
the paper sheet printed by the line head 60 to the switchback unit
8. The third conveyor 9 conveys the paper sheet switched back by
the switchback unit 8, and returns the paper sheet to the upstream
side of the line head 60. In duplex printing, the controller 1 sets
one of the front and back sides as the first side and sets the
other side as the second side. The controller 1 starts printing the
first side first. On the basis of the image data used for printing
the first side, the controller 1 determines the first ink quantity
as ink quantity to be ejected to the first area G1 on the first
side. The controller 1 determines the second ink quantity as ink
quantity to be ejected to the second area G2 as a backside area of
the first area G1 on the second side. When the first ink quantity
is more than the second ink quantity, the controller 1 controls to
perform the jam prevention printing. When the first ink quantity is
less than the second ink quantity, the controller 1 controls to
perform the normal duplex printing. When performing the jam
prevention printing, the controller 1 determines the absolute value
of a difference between the first ink quantity and the second ink
quantity. The controller 1 controls the line head 60 to perform
printing of the first area G1 by the same ink quantity as the
absolute value when printing the first side first time. The
controller 1 controls the switchback unit 8 to switchback the paper
sheet after printing the first side, so as to return the
switched-back paper sheet to the upstream side of the line head 60.
Next, the controller 1 controls the line head 60 to perform
printing the entire second side. The controller 1 controls the
switchback unit 8 to switchback the paper sheet after printing the
second side, so as to return the switched-back paper sheet to the
upstream side of the line head 60. Next, the controller 1 controls
the line head 60 to perform printing the remaining part on the
first side. The first area G1 is a strip-shaped area including a
side edge on the upstream side in the conveying direction of the
paper sheet when printing the first side, out of side edges facing
each other in the sub-scanning direction, and having a width in the
sub-scanning direction, which is a predetermined distance L1.
The jam prevention printing enables to divide the printing of the
first side into two times of printing. Only in cases where there is
high possibility of paper sheet jamming at the line head 60 due to
curl, the jam prevention printing can be performed. In the jam
prevention printing, in a first pass (pass of the paper sheet below
the line head 60), a part on the first side is printed, the entire
second side is printed in a second pass, and printing the entire
first side is completed in a third pass. As only a part of the
first area G1 is printed in the first pass, curl at the front edge
of the paper sheet (the downstream side in the conveying direction)
can be reduced in the second pass. Thus, paper sheet jamming hardly
occurs. In the second pass, ink is ejected to the second area G2
too. Due to the ejection to the second side (second area G2), the
edge on the second side is also bulged. As a result, curl at the
paper sheet edge is reduced. In other words, in the third pass for
duplex printing, curl at the edge on the downstream side in the
sheet conveying direction (front edge side in the sub-scanning
direction) is reduced. Therefore, paper sheet jamming at the line
head 60 can be prevented in the second pass and in the third pass.
It is not required to increase the number of passes to prevent
paper sheet jamming. Thus, the number of print passes can be
reduced. There is little reduction in productivity (the number of
printed sheets per unit time).
When performing the normal duplex printing, the controller 1
controls to print the first side first. When printing the first
side, the controller 1 controls the line head 60 to perform
printing the entire first side. The controller 1 controls the
switchback unit 8 (switchback roller pair 80) to perform the
switchback of the paper sheet after printing the first side, and
thus the switched-back paper sheet is sent back to the upstream
side of the line head 60. Next, the controller 1 controls the line
head 60 to perform printing the entire second side. When there is
little possibility of paper sheet jamming, the entire first side
can be printed in the first passing (pass) the line head 60. In
addition, the entire second side can be printed in the second
pass.
The controller 1 divides the determined first ink quantity by the
solid printing ink quantity 21 determined in advance so as to
determine the first ink quantity ratio. When the first ink quantity
is more than the second ink quantity, and when the determined first
ink quantity ratio is the predetermined reference ink quantity
ratio 22 or larger, the controller 1 controls to perform the jam
prevention printing. Even when the first ink quantity is more than
the second ink quantity, when the determined first ink quantity
ratio is smaller than the reference ink quantity ratio 22, the
controller 1 performs the normal duplex printing. Only when there
is a high probability of jamming of a curled paper sheet at the
line head 60, the jam prevention printing can be performed.
When performing the duplex printing, the controller 1 divides the
ink quantity ejected to the first area G1 by the solid printing ink
quantity 21 so as to determine the ink quantity ratio of the first
area G1. When the determined ink quantity ratio of the first area
G1 is the reference ink quantity ratio 22 or more, the controller 1
allows the paper sheet, which has been printed on the first side
first time and is on the way returning to the upstream side of the
line head 60, to wait at the switchback unit 8 (switchback roller
pair 80) for the predetermined wait time 23. As elapsed time from
ink ejection becomes longer, the curl amount becomes smaller in
general. When there is a high probability of paper sheet jamming at
the line head 60 in consideration of the quantity of ink ejected to
the first area G1, it is possible to allow the paper sheet to
temporarily wait (stop) at the switchback unit 8. When printing the
second side for duplex printing (in the second pass), curl at the
edge on the downstream side in the sheet conveying direction (front
edge side in the sub-scanning direction) can be reduced before the
paper sheet enters below the line head 60.
The conveying rotation body 50 is disposed between the line head 60
on the most upstream side in the sheet conveying direction and the
first conveyor roller pair 51 on the most downstream side in the
sheet conveying direction. The predetermined distance L1 is the
sheet conveying distance between the conveying rotation body 50 and
the line head 60 on the most upstream side in the sheet conveying
direction. The conveying rotation body 50 contacts the paper sheet.
While contacting with the conveying rotation body 50, the paper
sheet curl is suppressed. A part of the paper sheet, which has
passed the pair of conveying rotation bodies 50 and is not pressed
any more, is curled again. With this structure, the widths of the
first area G1 and the second area G2 in the sub-scanning direction
can be determined on the basis of the part curling after the paper
sheet passes the conveying rotation body 50 closest to the line
head 60 until it reaches the line head 60.
In the case of printing a plurality of paper sheets successively,
when the controller 1 sets the front side of the first sheet as the
first side, it sets the front side of every paper sheet as the
first side. When the back side of the first sheet is set as the
first side, the back side of every paper sheet is set as the first
side. A relationship between front and back sides of the printed
paper sheet can be unified for all paper sheets.
Although the variation of the present disclosure is described
above, the scope of the present disclosure is not limited to this,
and various modifications can be made within the scope of the
present disclosure without deviating from the spirit thereof.
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